Polyamide solution



Patented Aug. 25, 1942 POLYAMIDE SOLUTION .Franklin Traviss Peters,Wilmington, Del., as-

Signor to E. I. du Pont de Nemours & Company, Wilmington, Del., acorporation of Delaware No Drawing. Application July 6, 1939, Serial No.283,124

4 Claims. This invention relates to compositions of matter, and moreparticularly to new and useful fluid compositions comprising syntheticlinear polymers.

The synthetic linear polymers with which this invention is concerned arepolyamides of the types described in U. S. Patents 2,071,250, 2,071,-253, and 2,130,948. It is therefore to be understood that the expressionsynthetic linear polyamides, as used hereinafter, designates the saidgeneral types. A characteristic property of these polyamides is thatthey can be formed into filaments which can be cold drawn into fibersshowing molecular orientation along the fiber axis. These polyamides areespecially useful forthe preparation of fibers, bristles, ribbons,sheets, foils, and coatings on metal, paper, fabric, regeneratedcellulose, and the like. The polyame ides are of two' types, thosederived from polymerizable monoaminomonocarboxylic acids or theiramide-forming derivatives, and those derived from the reaction ofsuitable diamines with v suitable dicarboxylic acids or amide-formingderivatives of dibasic carboxylic acids. It will be noted that thepolyamides are derived from bifunctional amide-forming reactants. Onhydrolysis with mineral acids, the polyamides yield monomericamide-forming reactants. For example, a polyamide derived from adlamine-and a dibasic acid yields on hydrolysis with hydrochloric acidthe dibasic acid and the dlamine hydrochloride, Similarly an amino-acidtype polyamide yields an amino-acid hydrochloride.

Although the synthetic linear polyamides as a class are mierocrystallineand have fairly high and sharp melting points, they can be formed intomany useful objects without the use of solvents. This is accomplished byspinning, extruding, or otherwise forming the object from the moltenpolyamide. However, there are advantages in the use of solutions ratherthan molten compositions to achieve the fluid state necessary inlacquers, coating compositions, and dopes suitable for use in formingvarious objects, such as films, sheets, ribbons, bristles, andfilaments. Forexample, in coating fabrics, paper, or other materialswhich are charred or tendered by high temperatures, the use of asolution which can be applied and subsequently evaporated to .dryness ata relatively low temperature'does not cause deterioration of thematerial being coated. It is often desirable to prepare a fluidcomposition for use over a period of time, and in that event it isconvenient if the composition can be kept in the liquid state by storageat ordinary temperatures. The application of such solutions as lacquersor adhesives is .much more easily carried out by methods well known tothe art than is the application of a molten composition. Further, theincorporation of plasticizers or other modifying agents into polyamidesis more advantageously done by addition of the plasticizer to a solutionof the polyamide rather than to a molten polyamide, minimizing thetendency toward discoloration and decomposition which frequently occurswhen blending is done with a melt. Further, there is a tendency withcertain types of plasticizers and modifying agents to be less compatibleat the high temperatures required for blendiig in a melt, whereas theycan be readily incorporated in a polyamide solution at a lowtemperature. A ,still further advantage in the use of solutions lies inthe ease with which they can be cast into films or coatings of uniformthickness, which is mechanically more diificult to accomplish with amolten composition due to its relatively high viscosity.

The fiber-forming polyamides are generally insoluble in the more commonorganic solvents but are soluble in phenols and usually in certainorganic acids, e. g. formic and acetic. These solvents are of limitedutility, however, dueto their corrosive'nature, toxicity, and tendencyto degrade the polymers. Further, although films or coatings can be castfrom solutions in these solvents, films flowed or cast in accord withthe usual procedure for depositing films from film-forming materials aretranslucent or cloudy and are therefore of limited utility. Amongnon-acidic organic materials, butanol has been heretofore used with somesuccess as a solvent, but since the solutions generally form gels attemperatures below about C., it is necessary to use the solutions attemperatures above 80 C. Other non-acidic organic materials are lesseffective solvents than butanol. In contrast to butanoL-closely relatedalcohols show little or no solvent action on the polyamides with whichthis application is concerned. Chlorinated hydrocarbons also have littleor no solvent actionon these polymers.

This invention has as an object the preparation of new and improvedsynthetic linear polyamide compositions useful inmaking filaments,bristles, ribbons, films, sheets, and coatings on metal, fabric, paper,regenerated cellulose, and the like.

This and other objects which will be apparent from the followingdescription, areaccomplished by dissolving the polyamide in a volatilesolvent mixture comprising an alcohol and a halogenated hydrocarbon.

I have now found that mixtures of halogenated hydrocarbons with.alcohols are very active sol vents for the above mentioned polymers andthat tures of methanol and chloroform readily dissolve these polyamides,frequently at room temperature and usually at temperatures only slightlyabove room temperature.

In the practice of this invention a variety of halogenated hydrocarbonsand alcohols can be used. The concentration of the polymers which can beobtained in solution and the viscosity of the solution depend upon thenature of the polymer used, the nature of the solvent components, theproportions of the solvent components, and the temperature. Thisinvention is particularly advantageous in connection with theinterpolyamides, i. e. polyamides derived from a, mixture ofpolyamide-forming compositions, since solutions of these polymers can beobtained in the highest concentrations. amides the most soluble arethose having hydrocarbon radicals as lateral substituents, as forinstance those derived from such diamines as 2,5- dimethylhexamethylenediamine or 2-tertiary butylhexamethylene diamine, or from such acids asa-a-dimethyl adipic acid or a-tertiary butyl adipic acid.

Among the alcohols which may be used as solvent components, methanolcontributes the greatest solvent or dispersing effect, and there isv agradual decrease in the solvent eifect contributed by alcohols ofincreasing molecular weight. Among the halogenated hydrocarbons whichmay be used as solvent components, chloroform and other compounds whichcontain a halogenated alkyl group which retains only one hydrogen atomcontribute the maximum solvent or dispersing eflect. The most desirablecombination of solvent components in a given case will depend on thenature of the polymer and, to a certain extent, on the nature of theother ingredients present, such as plasticizers, pigments, and the like.Depending upon the nature of the polymerv and the solvent componentsused, the weight ratio of halogenated hydrocarbons to the alcohols usedin admixture as solvents may be conveniently varied between 1:9 and 9:1,the preferred range being from 2:1 to 4:1. The toughne clarity, andother properties of films, fibers, and other objects formed byevaporation or coagulation of the polyamide solution vary somewhat withthe ratios of the solvent components. It is frequently advantageous touse more than one alcohol in admixture with a halogenated hydrocarbon.

This is particularly true when certain plasticizers are added to thesolution. With some plasticized compositions, clear films or coatingscan be obtained from the solutionsonly when more than one alcohol ispresent in the solution. Similarly, it is sometimes advantageousto use aplurality of halogenated hydrocarbons in admixture with one or morealcohols. It is also frequently use- Of the simple polyful to adddiluents, which have no tendency to increase the solvent action ofthemixture, but

may aid in promoting the clarity, of objects formed by act as blendingagents for the polyamide and plasticizers or othermodifying agents.Aromatic hydrocarbons, e. g. benzene and toluene, are examples ofdiluents which may be used for these compositions.

In most cases thesolutions can be conveniently prepared by agitating thepolymer with the solvent mixture at roomtemperature or at a slightlyhigher temperature, although it is frequently advantageous to'agitatethe polymer with the solvent at the boiling point of the solvent under areflux condenser.- A given solvent mixture may have only a swellingaction on a given polymer at room temperature, forming a rigid ornon-fluid gel. A gel of this type can usually be dispersed to a fluidsolution by raising the temperature. Solutions prepared in this mannerwill solidify again to a gel after cooling to room temperature or belowthe minimum temperature required to effect solution originally. The timeinterval which elapses before a gel is formed varies with the nature ofthe polymer, the solvents, plasticizers, and other materials present inthe composition. In some cases such super cooled solutions can behandled at room temperature for as long as several days before gelformation occurs. In other cases a gel may be formed within severalminutes after cooling to room temperature. When the solutions are usedto form films, fibers, coatings, or other objects by a process involvingsolvent evaporation it is frequently advantageous to cool the solutionsto temperatures in the range where gel formation can eventually occurbut is sufliciently delayed to permit the casting, coating, or desiredmanipulation to be carried out while the composition is still fluid,since in this unstable condition the solutions than at the temperatureswhere gel formation cannot occur. The increased viscosity is ofparticular advantage when the solutions are cast or applied as thickcoatings or films since a viscous coating will maintain its shape in thetime interval required for solvent evaporation to produce aself-supporting coating or film. It is often possible by continuedagitation of a super-cooled solution to prevent the formation of a gelat temperatures below which gel formation would otherwise occur, andthis procedure can be used to advantage in practicing the presentinvention. This invention is described more specifically in thefollowing examples, in which parts are expressed by weight.

Example I One hundred fifty parts of an interpolyamide (intrinsicviscosity 1.29) prepared from hexamethylenediammonium adipate (saltderived from hexamethylenediamine and adipic acid) and caprolactam inthe weight ratio of 3 to 2 was dissolved in a mixture of 900 parts ofchloroform and 240 parts of methanol by heating and stirring .under arefiux condenser. The clear solution thus obtained was stored for 3 daysat 50 C., during which time it remained fluid. At various intervalsduring this storage period portions of the solution were cooled to roomtemperature and fiowed in a'uniform layer on a metal casting plate at 20C. by means of a leveling blade set at 0.0065 in. The casting platetemperature was maintained at 20 C. until the solvents hadevapevaporation of the solvents, or may generally have a higherviscosity- 2,293,760 3. orated sufficiently to give a film which was dryto the touch (about minutes). To dry the film furtherjthe-plate washeated at 4045? C. for 6 minutes and then at 100 C. for 10 minutes witha draft of hot aifcir'culating above the film. The film was thenstripped from the casting plate and finally stored in anoven at 65 C.for

at least 12 hours to remove traces of solvent.

Films 0.00083 in. thick which were cast by this procedure had averagetensilestrengths (based on the original dimensions) of 7000 lbs. per sq.in. and elongations of 632%, both of which were measured on the standardScott Tensile Strength machineat 77 F. and 50% relative humidity.

Example II Five parts of an interpolyamide (intrinsic vis-' Example IIITwo hundred parts of an interpolyamide (intrinsic viscosity 1.03)prepared from equimolecular quantities of hexamethylenediammonium Asexamples of additional synthetic linear polyadipate anddecamethylenediammonium sebacate was stirred at 60 C. for two hours with240 parts of methanol, 220 parts of trichloroethylene, 100 parts of2-bis-parahydroxyphenylpropane, and 100 parts of the mixture of N-ethylparaand ortho-toluenesulfonamides which is commercially known asSantlcizer #8. The resulting solution was then mixed at 60 C. with 235parts of a pigment dispersion consisting of 133 parts of a mixture ofsolid pigments, 53 parts of methanol, an 49 parts of trichloroethylene.The pigmente solution was then cooled to -45 C. and coated on fabric atthis temperature.

Example IV One part of a polyamide (intrinsic viscosity 0.54) preparedfrom 2,5-dimethylhexamethylenediamine and a, e'-dimethyl adipic acid wasdissolved in a mixture of 6 parts of chloroform and, 1.8 parts ofmethanol by stirring at room temperature. The resulting thin solutionwas applied with -a brush as a clear lacquer over metal, wood, and glasssurfaces.

Example I! through a zone of air heated to 90 C. so that a"- tough,adherent, transparent coating 0.0004 in.

. thick was obtained.

Example VI An ester-amide interpolymer (intrinsic viscosity 0.80), wasprepared from 30 parts of hexamethylenediammonium sebacate and 70 partsof an equimolecular mixture of 2,2-dlmethyl propanediol [HOCI-IrC(CI-Iz)zCHzOH] and sebacic acid. Ten parts of this polymer was dissolved in amixture of parts of dichloromethane and 16 parts of from the combinationof ethanol by warming to 40 C. After the solution was cooled to 20 C.films; were cast by a procedure isimilarto that vdescribed;in Example I.When tested on' the'standard Scott Tensile '5 Strength. machine at '77Ffand 50% relative humidity, the films (0.0008 in. thick) had a tensilestrength of'2,000.pounds per sq. in. (based on original dimensions) andan elongation of 540%.;

The interpolymer solution was also suitable for similar to that bywhichcellulose acetate filaments are spun. Upon cold drawing these inter-Further examples of valuable solutionsv of ester-amide interpolymers forfilm casting, fabric coating, adhesive uses, etc., are those indicatedbelow:

Per cent Polymer Solvents (ratio by Wt.) polymer in V solutionPolyhexamethylene 'adlpam- Methanol (16) tggi g ggy adlpateTrichloroethylene (l5). 40

' Polyhexamethylene adipam-v Methanol (8).'

ide-polyethylene adipate Ohloroform (l5) 22 ester). n-Butanol (1.6)

mers which can be dissolved in solvent mixtures comprising halogenatedhydrocarbons and alco hols, there may be mentioned polyamides derivedfrom the combination of a'dibasic acid and 35 a diamine, at least one ofwhich and preferably both of which reactants are substituted with atleast one alkyl group in the hydrocarbon chain. Interpolyamides derivedfrom the combination of two or more diamines with two or more di- 4basic acids are particularly well adapted to the preparation of thesesolutions. As examples of polyamidesxof this type which may be used maybe mentioned those derived from the combination of any two or'more ofthe following diamines 45 with any two or more of' the following dibasicacids:

Tetramethylenediamine Adipic acid Pentamethylenediamine Sebacic acidHexamethylenediamine 1' Suberic acid Octamethylenediamine Carbonic acidDecamethylenedi'amine Azelaic acid D-Xylylenediamine lm-Phenylenediamine 55 3,3'-diaminodipropyl ether 60 more diamines' andone or more dibasic' acids are also excellently adapted to thepreparation of solutions of the type described in this invention. Asexamples of polyamides'of this type which may be used may be mentionedthose derived (i-amino-caproic acid, 9-aminononanoic acid, ll-aminoundecanoic acid, or one of their amide-forming derivatives with one or moreof the diamines mentioned in the table just preceding and with one ormore of the 70 acids mentioned in the same table.

In addition to using the polymers mentioned above which are obtainablefrom bifunctional polyamide-forming reactants, as essentially solereactants, the use of linear polymers obtained by including withpolyamide-forming reactants 10 spinning filaments by a dryspinningtechnique simple polyamides.

methylenediammonium adipate with diethylene glycol and adlpic acid,hexamethylenediammonium adipate with dimethyl dimethylolmethane andadipic acid, hexamethylenediammonium sebacate with ethylene glycol andsebacic acid, and decamethylenediammonium sebacate with ethylene glycoland sebacic acid.- Further examples of modified polyamides to which thepresent invention is applicable are those derived from amino acids,dibasic acids, and glycols; those derived from amino acids and hydroxyacids; and those derived from diamines, dibasic acids and hydroxy acids.The invention is also applicable to mixtures of polyamides. In general,the synthetic linear polymers do not possess fiber-formcosity above 0.4.Therefore, to be useful in making fibers or likewise in making films,ribbons, tough coatings, etc., the polyamide should have an intrinsicviscosity above 0.4 and preferably above 0.6. The expression, intrinsicviscosity, is to be understood in accordance with the definition thereofcontained in U. S. Patent 2,130,948.

ing properties unless they have an intrinsic vis- As additional examplesof halogenated hydrocarbons which may be used in admixture with one ormore alcohols to prepare polyamide solutions may be mentioned carbontetrachloride, 1,2-dichloroethane, ethylidene dichloride, symmetricaldichloroethylene, unsymmetrical dichloroethylene,1-dichloro-2-chloroethane, l-trichloroethane, tetrachloroethane,tetrachloroethylene, and chlorobenzene. Chlorinated ethers, such as Jfl'-dichloroethyl ether, may also be used. Although the chlorinatedhydrocarbons are in general preferred, other halogenated hydrocarbonsmay be used, suitableexamples being ethylene dibromide, bromoforrn, andfluorobenzene.

As additional examples of alcohols which may be used in admixture withone or more halogenated hydrocarbons to prepare polyamide solutions maybe mentioned n-propanol, isopropanol, isobutanol, tertiary butanol, thevarious amyl alcohols, and benzyl alcohol. The preferred alcoholscontain less than five carbon atoms. Ether alcohols, such as,B-methoxyethanol, may be used. Keto alcohols, such as diacetonealcohol, are also useful. Polyhydric alcohols, e. g. ethylene glycol,can be used but are less preferred because of their high boiling points.

The properties of objects formed from the compositions described hereinmay be modified and are frequently rendered more useful by the additionof plasticizers and pigments. The compositions of this invention mayalso contain other types of modifying agents, such as resins, cellulosederivatives, and other film-forming materials, waxes, water-repellents,luster modifying agents, dyes, antioxidants, oils, antiseptics, etc.

The present solutions of polyamides in mixtures of volatile halogentedhydrocarbons and volatile alcohols are useful for forming a variety ofobjects by a process of solvent evaporation. Typical objects which canbe formed from these solutions by solvent evaporation are fibers,filaments, bristles, surgical sutures, fishing leaders, fishline, dentalfloss, films, ribbons, sheets, safety glass interlayers, golf ballcovers, and plasticized or otherwise modified solid compositions usefulin making molded articles. The solutions are useful for application aslacquers on wood, metal, glass, and other surfaces, for coating wire,fabrics, paper, regenerated cellulose, and the like, and forimpregnating fabric, paper, etc.

The advantages which these solutions possess over synthetic linearpolyamide solutions previously proposed in the art that they aresubstantially non-corrosive, are fluid at relatively low temperatures,and can be evaporated at relatively low temperatures, givingtransparent, homogeneous films, fibers, and other objects. Moreover, thesolvent mixtures of this invention do not materially degrade thepolyamides even during storage for long periods of time, although thereis some evidence of reaction when the solutions are heated.

As many apparently widely different embodiments of this invention may bemade -without departing from the spirit and scope thereof, it is to beunderstood that I do not limit myself to the specific embodimentsthereof except as defined in the appended claims.

I claim:

1. A composition of matter comprising a solution of synthetic linearpolyamide in a solvent mixture comprising, in 1:9-9:1 weight ratiorange, alcohol and halogenated hydrocarbon; the said polyamide being thereaction product of a polymer-forming composition comprising a diamine,a dibasic carboxylic acid and a monoaminomonocarboxylic acid.

2. The composition set forth in claim 1 in which the said halogentedhydrocarbon is a chlorinated hydrocarbon.

3. The composition set forth in claim 1 in which the said solventmixture comprises trichroroethylene and methanol.

4. A composition of matter comprising a solution of synthetic linearpolyamide in a solvent mixture comprising, in 1:9-911 weight ratiorange,'alcohol and halogented hydrocarbon, the said polyamide being thereaction product of a polymer-forming composition comprisinghexamethylenediammonium adipate and caprolactam FRANKLIN TRAVISS PETERS.

